Metrology part 1:definition of quality criteria

Any measurement is always afflicted with some degree of uncertainty. A correct understanding of the different types of uncertainty, their naming, and their definition is of crucial importance for an appropriate use of measuring instruments. However, in perioperative and intensive care medicine, the metrological requirements for measuring instruments are poorly defined and often used spuriously. The correct use of metrological terms is also of crucial importance in validation studies. The European Union published a new directive on medical devices, mentioning that in the case of devices with a measuring function, the notified body is involved in all aspects relating to the conformity of the device with the metrological requirements. It is therefore the task of the scientific societies to establish the standards in their area of expertise. Adopting the same understandings and definitions among clinicians and scientists is obviously the first step. In this metrologic review (part 1), we list and explain the most important terms defined by the International Bureau of Weights and Measures regarding quantities and units, properties of measurements, devices for measurement, properties of measuring devices, and measurement standards, with specific examples from perioperative and intensive care medicine

Metrology part 2:Procedures for the validation of major measurement quality criteria and measuring instrument properties

A measurement is always afflicted with some degree of uncertainty. A correct understanding of the different types of uncertainty, their naming, and their definition is of crucial importance for an appropriate use of the measuring instruments. However, in perioperative and intensive care medicine, the metrological requirements for measuring instruments are poorly defined and often used spuriously. The correct use of metrological terms is also of crucial importance in validation studies. The European Union published a new directive on medical devices, mentioning that in the case of devices with a measuring function, the notified body is involved in all aspects relating to the conformity of the device with the metrological requirements. It is therefore the task of scientific societies to establish the standards in their area of expertise. After adopting the same understandings and definitions (part 1), the different procedures for the validation of major quality criteria of measuring devices must be consensually established. In this metrologic review (part 2), we review the terms and definitions of validation, some basic processes leading to the display of an indication from a physiologic signal, and procedures for the validation of measuring instrument properties, with specific focus on perioperative and intensive care medicine including appropriate examples

From cardiac output to blood flow auto-regulation in shock

Shock is defined as a state in which the circulation is unable to deliver sufficient oxygen to meet the demands ofthe tissues, resulting in cellular dysoxia and organ failure. In this process, the factors that govern the circulation ata haemodynamic level and oxygen delivery at a microcirculatory level play a major role. This manuscript aims toreview the blood flow regulation from macro- and micro-haemodynamic point of view and to discuss new potentialtherapeutic approaches for cardiovascular instability in patients in cardiovascular shock. Despite the recent advancesin haemodynamics, the mechanisms that control the vascular resistance and the venous return are not fully understoodin critically ill patients. The physical properties of the vascular wall, as well as the role of the mean systemicfilling pressure are topics that require further research. However, the haemodynamics do not totally explain thephysiopathology of cellular dysoxia, and several factors such as inflammatory changes at the microcirculatory levelcan modify vascular resistance and tissue perfusion. Cellular vasoactive mediators and endothelial and glucocalixdamage are also involved in microcirculatory impairment. All the levels of the circulatory system must be taken intoaccount. Evaluation of microcirculation may help one to detect under-diagnosed shock, and together with classichaemodynamics, guide one towards the appropriate therapy. Restoration of classic haemodynamic parameters isessential but not sufficient to detect and treat patients in cardiovascular shock.Shock is defined as a state in which the circulation is unable to deliver sufficient oxygen to meet the demands ofthe tissues, resulting in cellular dysoxia and organ failure. In this process, the factors that govern the circulation ata haemodynamic level and oxygen delivery at a microcirculatory level play a major role. This manuscript aims toreview the blood flow regulation from macro- and micro-haemodynamic point of view and to discuss new potentialtherapeutic approaches for cardiovascular instability in patients in cardiovascular shock. Despite the recent advancesin haemodynamics, the mechanisms that control the vascular resistance and the venous return are not fully understoodin critically ill patients. The physical properties of the vascular wall, as well as the role of the mean systemicfilling pressure are topics that require further research. However, the haemodynamics do not totally explain thephysiopathology of cellular dysoxia, and several factors such as inflammatory changes at the microcirculatory levelcan modify vascular resistance and tissue perfusion. Cellular vasoactive mediators and endothelial and glucocalixdamage are also involved in microcirculatory impairment. All the levels of the circulatory system must be taken intoaccount. Evaluation of microcirculation may help one to detect under-diagnosed shock, and together with classichaemodynamics, guide one towards the appropriate therapy. Restoration of classic haemodynamic parameters isessential but not sufficient to detect and treat patients in cardiovascular shock

Dynamic arterial elastance as a predictor of arterial pressure response to fluid administration: a validation study.

INTRODUCTION: Functional assessment of arterial load by dynamic arterial elastance (Eadyn), defined as the ratio between pulse pressure variation (PPV) and stroke volume variation (SVV), has recently been shown to predict the arterial pressure response to volume expansion (VE) in hypotensive, preload-dependent patients. However, because both SVV and PPV were obtained from pulse pressure analysis, a mathematical coupling factor could not be excluded. We therefore designed this study to confirm whether Eadyn, obtained from two independent signals, allows the prediction of arterial pressure response to VE in fluid-responsive patients. METHODS: We analyzed the response of arterial pressure to an intravenous infusion of 500 ml of normal saline in 53 mechanically ventilated patients with acute circulatory failure and preserved preload dependence. Eadyn was calculated as the simultaneous ratio between PPV (obtained from an arterial line) and SVV (obtained by esophageal Doppler imaging). A total of 80 fluid challenges were performed (median, 1.5 per patient; interquartile range, 1 to 2). Patients were classified according to the increase in mean arterial pressure (MAP) after fluid administration in pressure responders (≥ 10%) and non-responders. RESULTS: Thirty-three fluid challenges (41.2%) significantly increased MAP. At baseline, Eadyn was higher in pressure responders (1.04 ± 0.28 versus 0.60 ± 0.14; P < 0.0001). Preinfusion Eadyn was related to changes in MAP after fluid administration (R (2) = 0.60; P < 0.0001). At baseline, Eadyn predicted the arterial pressure increase to volume expansion (area under the receiver operating characteristic curve, 0.94; 95% confidence interval (CI): 0.86 to 0.98; P < 0.0001). A preinfusion Eadyn value ≥ 0.73 (gray zone: 0.72 to 0.88) discriminated pressure responder patients with a sensitivity of 90.9% (95% CI: 75.6 to 98.1%) and a specificity of 91.5% (95% CI: 79.6 to 97.6%). CONCLUSIONS: Functional assessment of arterial load by Eadyn, obtained from two independent signals, enabled the prediction of arterial pressure response to fluid administration in mechanically ventilated, preload-dependent patients with acute circulatory failure